If you tend to take selfies of an amorous or suggestive nature, you might want to think twice before selling your old smartphone, as one prominent computer security firm cautions that not even wiping the device’s data and performing a factory reset guarantees that your old files and personal information will be inaccessible to the new owner.

In a blog entry posted last week, Jude McColgan of Avast Software explained that the company purchased 20 used Android smartphones through an online auction website, then used “simple and easily available” recovery software to gain access to a truly astonishing amount of deleted files, including over 40,000 stored photographs.